Butylene dehydrogenation process



M.- W. MAYER BUTYLENE DEHYDROGENATION PROCESS Filed Feb. 15, 1945 2 Sheats-Shegt 1 hwifom cozucwmohwmsmo cozucmwobgswe cozusmwobwumau m. C I 0m mm $5 2m cozocczuubu v f. 532 2: o @u cozoozum ocean-2am WI'TORMEY;

Patented Sept. 2, 1947 orrlcs BUTYLENE DEHYDROGENATKON PROCESS Maurice W. Mayer, Baytown, Elem, assignor to. Standard Oil Development @ompany, a corporation of Delaware Application February 16;, 19%, Serial No. 578,321

Claims. (El. 260-680) This application is a continuation-in-part of tanes to a catalytic dehydrogenation unit for the purpose of obtaining the highest possible yield of butadiene. This mixed feed stock is conventionally used because it is not commercially feaslble-to pretreat the feed. stock to eliminate all of the constituents except the butylenes. The isobutylene and normal butane produce substantially no butadiene when undergoing dehydrogenation and may be consideredmerely as diluents or impurities for the preferred reaction.

As only a portion of the butylene fed into a catalytic dehydrogenation unit is converted to butadiene each time it is passed over the dehydrogenation unit, it is conventional to pass the product to a, fractionation zone for the purpose of discarding hydrocarbons including propane and lighter hydrocarbons and polymer which may be formed in the process and to segregate a Ca hydrocarbon fraction for the purpose of removing therefrom the converted butadiene and admin the remainder with the fresh feed stock and again pass itthrough the dehydrogenation unit. Due to the fact that butylenes are removed from the mixture fed the dehydrogenation units at a higher rate than the isobutylene and butane,

these impurities tend to build up in the C4 fraction as the process continues. In order to maintain the concentration of the butane and isobutylene sumciently low to obtain satisfactory yields of butylene from the process, it is usual to bleed ofi a portion of the mixed material from which the butadiene has been extracted. Failure to bleed ofi a predetermined portion allows the concentration of the undesired butane and isobutylene to build up to a point which prevents the process from being commercially attractive.

On the other hand, the material bled ofi from ..'the recycled stock contains substantial amounts or normal butylene in addition to the undesired butane and isobutylene and these normal butylenes withdrawn from the system are, of course,

no longer available for conversion to butadiene. In accordance with the present invention the fresh feed stock coming into the system is fed into a catalytic unit maintained under conditions to obtain optimum dehydrogenation of the'normal butylene to butadlene and the recycle stock is red to the remaining catalytic units which are maintained under conditions which will not only cause dehydrogenation of the normal butylene to butadiene, but in addition will cause a substantial cracking of the normal butane and isobutylene. This arrangement greatly reduces the rate at which the concentration of butane and isobutylene build up in the recycle stock and greatly reduces or substantially eliminates the amount of recycle stock which must be bled ofi to maintain the concentration of the undesirable butane and isobutylene below the preselected value.

,Other objects and advantages of the present invention may be seen from reading the following description taken in conjunction with the drawing in which,

Figures 1 and 2 are in the form of diagrammatic flow sheets illustrating methods of practicing the present invention.

Turning now to the drawing and first to'Fig. 1, a mixture of hydrocarbons comprising normal butylene, isobutylene and normal butane is withdrawn from storage vessel It through line l2 into concentrating means l3.- A suitable method of concentrating the normal butylenes in the fraction is by the extraction and distillation of the mixture. Methods of concentrating mixtures of hydrocarbons are well known to the art and, accordingly, will not be described in any greater detail. The impurities from the concentratin means it are withdrawn via line l4 and the fraction in which the normal butylenehas been concentrated is withdrawn by line l5 and passed through heater it into catalytic dehydrogenation ing the more active catalyst and maintained under the lowest temperatures. The other units I8 and it contain less active catalyst and are operated at higher temperatures. A manifold 20 is arranged to supply steam to all of the catalytic units.

The product from catalytic unit ll isremoved via manifold M to fractionation zone 22 wherein, by suitable adjustment or temperature and pressure by means not shown, propane and lighter hydrocarbons are discarded from the system by way of line 23 and any polymer which may b formed in the reaction by way of line 24. A 04 fraction In accordance with is recovered by way of line 25 and routed thereby to extraction unit 26 for separation of the butadiene contained therein. It is understood, of course, that fractionation zone 22 may include a.plurality of fractionation towers. For convenience in the present description fractionation zone 22 is shown as a single unit. The butadiene is recovered from extraction unit 26 by way of line 21 while the remaining hydrocarbon mixture may flow through recycle line 28 and heater 29 into manifold. 3|]- where it is divided, with one porin order to maintain the concentration of thebutane and isobutylene below a predetermined value. a

The dehydrogenation units [6 and i9 are maintained at higher temperatures than is unit l1 so that there is not only conversion of normal butylene to butadiene, but in addition cracking of substantial amounts of normal butane and isobutylene to remove them from the system. It will be evident that by maintenance of suitable conditions in units I8 and I9 sufficient butane and isobutylene may be destroyed to make unnecessary any bleeding of recycle stock through outlet 3 I. Generally, however, it is undesirable to maintain such rigorous conditions in catalytic units 18 and I9 and accordingl small amount of mixed hydrocarbons will usually be bled ofi from the recycle line through outlet 3 I For example, the normal floutylene concentration in the fresh feed stock may be of the order of magnitude of 90% and that in the cycle stock coming from extraction step 26 may be 70%. In strictly catalytic dehydrogenation conversion, approximately 30% of the butylenes disappear with each pass with 70% converted to butadiene. However, only about /7 of the isobutylene and V3 of the normal butane are destroyed under the conditions whereby the normal butylene is converted to optimum amounts of butadiene using a fresh catalyst bed. It will be evident that to prevent the relative increase of the isobutylene and normal butane in the. recycle stock, at least 30% of the combined volumes of these impurities should be destroyed at each pass. It is generally undesirable to destroy such amounts by cracking even at higher temperatures in the catalytic chambers l1, l8 and I9, and, accordingly, the preferred mode of operation includes the drawing off of a small portionof the recycle stock as well as the employment of temperatures in vessels l8 and I9 sumciently high to destroy substantial amounts of isobutylene and normal butane by cracking.

A largenumber of dehydrogenation catalysts are known to the art suitable for employment in the catalytic units I1, 18 and I9. Particularly good results are obtained when using a dehydrogenation catalyst containing approximately 80% MgO, 14% iron oxide as an active ingredient, 3%

K20 as a promoter for the water gas reaction which is utilized in regeneration of the catalyst and 3% CuO as the stabilizer. It will be understood that the iron oxide may exist in diflferent degrees of oxidation from FeO to FezOs. Such a dehydrogenation catalyst is described in U. S-. patent application Serial No. 430,873, filed February 14, 1942. This catalyst, when fresh; will dehydrogenate very satisfactorily at atemperature of 1150 F. As the activity of the catalyst decreases, however, it is desirable to increase progressively the temperature of operation to upwards of 1300 F. In employing this catalyst it is desirable to employ steam heated to a temperature of approximately 1400 F. in conjunction with the hydrocarbon which is heated separately to a maximum temperature ofabout 1200 F. When employing three catalytic dehydrogenation chambers corresponding to units l1, l8 and 19 in Fig. 1, it is desirable to operate unit I! at a temperature of approximately 1150 F. and the remaining units at higher temperatures ranging from 1200" to 1300" F'.

Under some conditions. it may ,be desirable. not only to feed fresh feed stock to the most active catalyst bed, but in addition to admix feed stock with the recycled stock sent to the less active catalytic beds. When the feed stock is admixed with the recycled stock sent to the less active beds in the system, it is desirable to increase progressively the ratio of recycled stock to the feed stock charged to the less active catalytic beds which are operated at progressively higher temperatures. An arrangement suitable for carrying out this operation is illustrated in Fig; 2.

In Fig. 2 a mixture of hydrocarbons comprising normal butylene, isobutylene and normal butane is withdrawn from storage tank H and passed through line l2 to concentrating means l3 where a fraction is separated and removed via line H and the fraction comprising a major portion of normal butylene with minor portions of isobutylenes and butanes is withdrawn byline l5 and passed through heater l6. From heater I 6 a portion of the fraction is passed through line 32 and manifold 33 to the catalytic chamber containing fresh catalyst while the remainder may be fed selectively to the remaining catalytic chambers. Manifold 34 is arranged for supplying steam to the catalytic chambers.

' The hydrocarbon fractions resulting from the catalytic dehydrogenation carried on in vessels 35, 36, 31' and 38 may be withdrawn to fractionation zones 39, 40, 4| and 42 where propane and lighter, hydrocarbons are discarded by way of lines 39.; 40', 4| and 42' and polymer, which may have formed in the dehydrogenation reaction zones, may be discarded by way of lines 43, 44, 45 and 46. A fraction comprising essentially normal butane, isobutylene and butylenes discharges from the fractionation zones 39, 40, 4| and 42 by way of lines 41, 48, 49 and 50, respectively, into extraction vessels 5|, 52, 53 and 54 where the butadiene is separated therefrom and removed via lines 55, 56, 51 and 56. The remaining hydrocarbons from extraction vessels 5| to 54, inclusive, may be selectively passed into recycle lines 59, 66 and BI containing heaters 62, 63 and 64, respectively, by means of manifolds 65, 66, 51 and 68. Drawofi lines 65", 66', 61' and 68 are provided in the manifolds 65, 66, 61 and 68, respectively, for bleeding 01f as much of the recycled hydrocarbon mixture as may be necessary to'maintain the concentration of isobutylene and butane in the recycle stock below a desired value. Manifolds 69, 16, H and 12 are arranged to connect selectively lines 59, 60 and 6| to catalytic reaction vessels 35, 36,31 and 38.

It will be apparent that theseveral reaction vessels in Fig. 2 are arranged so. that the-flow of new charge stock and recycled charge steel; to the vessels may be proportioned .to allow the charging of fresh charge stock-tothe dehydroggenation vessel containing the most active cataecaees alyst bed and the progressive increase of the ratio of recycled stock to the fresh ieed in'the progressively less active catalyst beds. It will also be evident that the temperture of the catalytic bed, as well as the amount of recycled stock bled off through. lines 66', 67! and '68 may be regulated to maintain the optimum operating temperatures in the "catalytic beds while removing minimum amounts of recycled stock from the system to maintain the concentration of the normal butane and isobutylene in the charge stock below a predetermined value.

From the above description it will be seen that the practice of the present invention gives an improved yield of butadiene from a feed stock containing isobutylene and normal butane as impurities or diluents; The fresh charge containing the largest amounts of normal butylene is subjected to catalytic dehydrogenation under low temperature conversion conditions which reduces the amount of cracking of the butylene to a minimum. The recycled stock containing substantially larger amounts of contaminating isobutylenes and butanes and smaller amounts of the valuable normal butylenes is subjected to cracking conditions to destroy the isobutylenes and butanes. This arrangement reduces or eliminates the necessity for bleeding off recycle stock containing the valuable butylenes in order to keep the concentration of the isobutylene and normal butane. below a desired value.

While I have given specific examples showing the practice of the present invention, it is to be be made without departing from the scope of the invention.

Having fully described and illustrated the practice of the present invention, what I desire to claim is:

1. In a catalytic process, the steps of passing a feed stock comprising normal butylene, isobutylene and normal butane to a first catalytic zone and there catalytically dehydrogenating the normal butylene to butadiene in the presence of fresh catalytic material, removing product, including propane, C4 hydrocarbons and polymer from said first catalytic zone and fractionating it to separate a C4 fraction comprising butadiene, isobutylene, normal butylene and normal butane, separating butadiene from said fraction, passing at least a major portion of the remainder of said fraction to a second dehydrogenation zone having a catalyst of the same type as employed in the first zone but less active, and conducting the operation in the second zone under temperature and pressure conditions to dehydrogenate substantial amounts of normal butylene to butadiene and to cause the destruction by cracking of substantial amounts of the isobutylene and normal butane present therein.

2. A method for converting hydrocarbons comprising the steps of passing a hydrocarbon mixture comprising a major amount of normal butylene and minor amounts of isobutylene and normal butane through a first catalytic zone in contact with substantially fresh catalyst under temperature and pressure conditions to cause a conversion of substantial amounts of normal butylene to butadiene and a small amount of cracking of said hydrocarbon mixture, removing llii product including propane, Ci hydrocarbons and polymer irom said first catalytic zone, and distilling to recover a Ci fraction including butadiene, butylene, isobutylene and normal butane, separating butadiene from said fraction, passing at least a major portion of the remainder of said fraction to a second catalytic zone containing catalyst of the same type but less active than that in said first catalytic zone, and there subjecting it to conditions capable oi dehydrogenating substantial amounts of normal butylene to butadiene and of cracking substantial amounts of isobutylene and normal butane, removing the product oi the reaction from said second cata- I and minor portions of isobutylene and normal butane, maintaining aseries of separate catalytic zones, with the first zone of the series provided with substantially fresh catalyst and operated under temperature and pressure conditions to cause dehydrogenation of substantial amounts of normal butylene to butadiene while producing a small amount of cracking and the remaining catalytic zones of the series containing less active catalyst than the first zone, the temperature of each zone of the series being greater than the temperature of the preceeding zone of said series, passing fresh feed stock through the first catalytic zone, removing product including propane, C11 hydrocarbons andadmixtures directly as a function of the temperature of the catalytic zone to which the admixture is charged.

5. A method for treating hydrocarbons including the steps of passing a fresh feed stock comprising a major portion of normal butylene and minor portions of isobutylene and normal butane into a first catalytic zone and contacting it with substantially fresh catalyst under temperature and pressure conditions to convert a substantial amount of normal butylene to butadiene with a small amount of cracking, removing product including propane, C4 hydrocarbons and polymer from the first reaction zone, distilling the product to discard propane and polymer and recovering a first C4 fraction including butadiene, separating butadiene from the first C4 fraction, admixing a portion of the remainder of the first C4 fraction with fresh charging stock and charging the mixture to a second catalytic zone containing the same type of catalyst as said first zone, but less active and maintained under higher temperatures than the catalyst in said first catalytic zone, removing product including propane, C4 hydrocarbons and polymer from the second catalytic zone, distilling said product to second C4 fraction including butadiene, separating butadiene from the second C4 fraction. mixing at least a portion of the remainder otthe second 04 fraction as recycle stock with fresh third catalytic zone, and distilling said product 7 to discard propane and polymer and to recover a third Cr fraction including butadiene, and

' separating butadiene from said third C4 fraction.

charging stock with a higher ratio of recycled 5 said mixture in said third catalytic zone with said catalyst, removing product including propane, C4 hydrocarbons and polymer from the Number MAURICE W. MAYER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date 2,378,649 Mattox June 19, 1945 

